Automatic film processor replenishment system

ABSTRACT

A control circuit, for automatically controlling chemical replenishment in a chemical-containing automatic film processor, includes an integrator circuit which receives signals related to the image density in a sheet of image bearing material being transported through the processor. The signal currents are integrated for a predetermined time interval, and upon elapse of said predetermined time interval a reference current source having a polarity opposite to that of the signal current is coupled to the input of the integrator to reduce the output of the integrator toward a reference level. A circuit is provided for generating a control signal which effects replenishment throughout the time period required to reduce the output of the integrator to the reference level.

United States Patent [191 Kinoshita et al.

[ AUTOMATIC FILM PROCESSOR REPLENISHMENT SYSTEM [75] Inventors: MinoruKinoshita; Osami Taniuchi,

both of Kyoto,'Japan- [73] Assignee: LogEtronics lnc., Springfield, Va.

[22] Filed: Nov. 2, 1973 [21] Appl. No.: 412,516

[44] Published under the Trial Voluntary Protest Program on January 28,1975 as document no.

[30] Foreign Application Priority Data Mar. 7, 1973 Japan 48-26197 [52]US. Cl. 354/298; 134/57 R [51] Int. Cl. G03D 13/00 [58] Field of Search354/297, 298, 299, 324;

[56] References Cited UNITED STATES PATENTS 3,559,555 2/1971 Street354/298 Developer Tank [ Dec. 16, 1975 Primary ExaminerFred L. BraunAttorney, Agent, or FirmElliott l. Pollock [5 7 ABSTRACT A controlcircuit, for automatically controlling chemical replenishment in achemical-containing automatic film processor, includes an integratorcircuit which receives signals related to the image density in a sheetof image bearing material being transported through the processor. Thesignal currents are integrated for a predetermined time interval, andupon elapse of said predetermined time interval a reference currentsource having a polarity opposite to that of the signal current iscoupled to the input of the integrator to reduce the output of theintegrator toward a reference level. A circuit is provided forgenerating a control signal which effects replenishment throughout thetime period required to reduce the output of the integrator to thereference level.

7 Claims, 9 Drawing Figures Light Source Control Circuit I ReservolrFixer Tank Light Sou ce F I6 I A H\ Control PE Light Receiver CircuitDeveloper I Tank E E E Wash Tank Fl M ow eter Valve J B} K C] ValveReservoir Fixer Ta nk) 0 M K SZeirtoRq 7 J PFIiG. A2; w r or r ;-ero|nqSensed Signal I Re Qy Replenishment Control Signal oo- Current Input 4 89 l 3 I E M Leve| w Control I 15% Detector Relay ES Integrator 2,3,4

Sensed Si nal Film-IO Curren 5i 1 N Dim ll FIG. 3A.

Period Susceptible To Leakage Current Integrator Output Voltage FIG. 38.T

Replenishment Control SignalE on on s v FIG. 3C. Off

U.S. Patent Dec.16, 1975 Sheet2af2 3,927,417

Replenishment I Reverse Polarity Cont ol Signal FIG. 4

lgete rlence Current I l mr 1 r---I 2e K I I i2 I I I l l l Life? Rele't s gg Petector Rela y R858? l Current ll'lDJT l 3 24 I Integratorl3,l4,l5,27 L 3 l l8 "1 L l x I Tim r COI'ITFOI l eve Zeming 9 RelayDetector Rem l6 y "OR"Gate 22 Sensed Signal Current Film 29 Fum 3O E Fl6. 5A. L A M Integrator Output I I I Voltage l I l l I I I I FIG. 5 B. Il I I I T n I L To i lo T5 Replenisnment I i l I Control Signal l I l ESon I On I I On FIG. 5C. Off I AUTOMATIC FILM PROCESSOR REPLENISHMENTSYSTEM BACKGROUND OF THE INVENTION This invention relates to a method ofreplenishing the processing liquid in an automatic film processor tocompensate for the lowered activity of the developer and fixer fluidswhich would otherwise result from the processing of exposed film.

Automatic film processors convey exposed films by appropriate transportmeans through a sequence of developing, fixing and washing baths.However, processing results are affected by at least four factors:developing time, developing temperature, degree of fluid agitation, andchemical activity of the processing liquid. Of these four factors, thedeveloping time, temperature and degree of agitation can be controlledrelatively easily by the incorporation of appropriate design featuresassociated with the mechanical construction of the automatic filmprocessor. Therefore, if the remaining factor, i.e., chemical activityof the processing liquid, can be maintained constant, then the overallfilm processing performance can be stabilized.

The concentration and activity of the processing liquid decrease as aresult of depletion caused by film development action and by chemicaloxidation and, in order to restore the concentration and activity, it iscommon practice to add appropriate amounts of replenishing fluid fromtime to time.

One commonly employed method of controlling replenishment depends uponthe establishment of a constant rate of flow of replenishing fluid, andcontrol of the duration of time during which the fluid is introducedinto the developing liquid. To practice this method a variety of meanshave been disclosed in the prior art. For example, one approach employsa sensing means at an appropriate position along the film transport pathto detect the physical passage of the length of film, thereby enablingreplenishment to be performed during travel of the film through thesensing station. This method delivers replenishing fluid to theprocessing liquid in an amount proportional to the length of film beingconveyed and is best suited to a situation where films of a definitewidth and average exposure are being processed because, when such asystem is used in the processing of sheet films of different sizes, eventhose films which are of equal area may result in different amounts ofreplenishment depending upon whether the minor dimension or the majordimension of the film sheet is sensed. Accurate replenishment rarelyresults from the use of such length-sensing systems.

An alternate method is designated dial-type replenishing wherein a dialsimilar to that of a telephone set is provided and an appropriatenumber, selected from a tabular chart depicting the size of the film tobe processed and its estimated degree of exposed area, is dialed in toset a synchronous timer, thereby allowing replenishment fluid to flow ata constant rate until the dial returns to its initial position. Thismethod is of practical utility, but the selection of numbers and dialoperations often tends to be inconvenient. In addition, certain modernprocess cameras for the graphic arts allow the film to be removed fromthe camera back automatically after exposure operations have beencompleted and then convey the film, by mechanical means, to theautomatic film processor. If the dial-type method is applied to such asystem, manual operation of the replenishing dial will be required foreach sheet of film to be processed, eliminating many of the benefits ofautomation.

To eliminate such drawbacks inherent in replenishment systems of theprior art an alternative technique has been developed wherein theblackened areas of the processed film are measured photoelectrically,and this information is then used to replenish the processing liquidaccording to the measured values. This approach employs a photoelectricmeans which views the entire width of the path through which theprocessed film passes, and which senses the interruption of measuringlight flux resulting from the passage of the blackened areas of thefilm, using this information to control the replenishingdevice. Systemsof this general type are disclosed, for example, in Street, et al., US.Pat. No.

3,554,109, and Street US. Pat. No. 3,559,555. The

present invention relates to an improvement of this type of replenishingtechnique, and has as an objective the elimination of disadvantagesinherent in the control circuits used heretofore, in order to provide apractical, accurate replenishing method.

SUMMARY OF THE INVENTION The replenishment system of the presentinvention is operative to automatically control chemical replenishmentin a chemical-containing automatic film processor. As film sheets aretransported through the processor,-the varying image densities in eachof said sheets are optically monitored throughout substantially theentire width and length of each sheet. The sensor employed to effectthis monitoring produces a signal which is coupled as one input to anintegrator circuit, and the integrator circuit is in turn associatedwith a timer operative to permit the integrator to accumulate andintegrate the sensing signal currents during a predetermined timeinterval. At the end of the predetermined time interval, the timeroperates to connect, to the input of the integrator circuit, a referencecurrent source having a polarity opposite to that of the sensing signalcurrent, and the reference source accordingly reduces the output of theintegrator circuit toward a reference voltage level. The time requiredto reduce the integrator circuit output voltage to the reference levelis jointly dependent upon the output level of the integrator circuit atthe time the reference source is connected to its input, and upon themagnitude of any sensing signal present at the input of the integratorcircuit during the time that the reference source is attempting toreduce the integrator circuit output to said reference voltage level. Areplenishment control signal is generated for a period of time whichcorresponds to the time-required to effect reduction of the integratorcircuit output to the reference level.

The integrator circuit, in its preferred form, includes an integratingcapacitor which is charged by the sensing signal input current, andwhich is differentially discharged by connecting the reference currentsource to a second input of the integrator. Since the improved system ofthe present invention contemplates that the capacitor of the integratingcircuit be periodically discharged to a reference voltage level, such asground potential, proper operation does not require the integratingcircuit capacitor to maintain a charge for any significant period oftime. The system operation is accordingly rendered independent of anyleakage of charge from the capacitor, thus providing for more accuratecontrol and replenishment than has been possible heretofore.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of anautomatic film processor incorporating the automatic replenishmentcontrol system of the present invention;

I FIG. 2 is a schematic block diagram of a prior art control circuitemployed in automatic replenishment control systems of the general typeshown in FIG. 1;

' FIGS. 3A, 3B and 3C graphically illustrate the operation of the priorart control system of FIG. 2;

FIG. 4 is a schematic block diagram of the control circuit of thepresent invention; and

FIGS. 5A, 5B and 5C graphically depict the operation of the circuitshown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring initially to FIG. 1,an automatic film processor incorporating the automatic replenishmentcontrol of the present invention may comprise a plurality of processortanks comprising at least one developer tank A, at least one fixer tankB, and at least one wash tank C. Exposed sensitized material to bedeveloped is fed in sequence through the tanks A, B, and C along a pathof the type generally designated D by means of an appropriate transportsystem diagrammatically illustrated by rollers. E. Squeegee rollers Fare located downstream of the wash tank C; and the developed film iscaused to pass through said squeegee rollers for partial drying,whereafter the film is fed through a drier G for final drying andsubsequent collection. Apparatuses of this general type are inthemselves well known.

A sensor arrangement, comprising a light source L and a photoelectriclight receiver PE, disposed respectively on opposing sides of the filmtransport path, is provided at a position between wash tank C and dryerG to determine the different image densities developed in differentareal portions of the film by the processor action; thereby to provide ameasure of the amount of chemical which has been used up in the courseof the development process. Such sensor arrangements may take variousforms, some of which are described and illustrated in Street, et al.,US. Pat. No. 3,554,109 and Street US. Pat. No. 3,559,555 and, in itspreferred embodiment, the sensing system is adapted to substantiallycompletely inspect each sheet in film throughout both its width andlength. The sensing signal produced by the sensor is coupled to acontrol circuit H (with which the present invention is primarilyconcerned), and the output of the control circuit selectively operates asolenoid controlled valve I adapted to permit the feeding ofreplenishment chemical from a reservoir or tank J via a manual shut-offvalve K, flowmeter M and line to the developer tank. A similararrangement may be provided to effect controlled replenishment of thefixer solution in tank B but, to simplify the drawings, this has notbeen shown in FIG. 1.

FIG. 2 is a block diagram showing the control circuit H of onereplenishment system of the prior art. The signal current Ei, obtainedfrom the photoelectric means PE (FIG. 1) in proportion to the blackenedareas of the film, is coupled to input terminal 1 and is accumulated inan integration circuit composed of resistor 2, DC amplifier 3 andcapacitor 4. When the output voltage E0 of the integration circuitreaches a predetermined magnitude, the level detector operates andcauses contacts 7 of zeroing relay 6 to close, thereby dissipating thecharge accumulated in capacitor 4 of the integration circuit.simultaneously timer 8 is actuated and, via control relay 9, generates asolenoid-valve control signal Es to initiate replenishment of theliquid. It can be seen, therefore, that the control circuit of FIG. 2,when used in the system of FIG. 1, causes a flow of replenishing fluidat a predetermined constant rate set by flowmeter M, for a predeterminedperiod of time established by timer 8, whenever the accumulated voltageEo resulting from sensing signal Ei, reaches the aforementionedpredetermined magnitude.

FIG. 3 is a chart showing the operating relationships between variouswaveforms associated with the device of FIG. 2. FIG. 3A shows typicalsensing signals Ei; FIG. 3B shows resultant integration circuit outputsE0; and FIG. 3C shows the related replenishment control signals Es. Dueto the input sensing signal Ei, the output E0 increases gradually and,after a definite integrated voltage level is reached, output E0 isreturned to zero and, at the same time, a replenishment control signalEs is produced for a predetermined period of time. Accordingly, thecircuit of FIG. 2 enables replenishment to be carried out automaticallyin proportion to the blackened areas of the film, and is generally veryeffective. However, a disadvantage is presented by the fact that, whenthe value of output voltage E0 accumulated in response to signals fromindividual films fails to reach said definite voltage level,replenishment of the liquid may be inaccurate. Such a condition couldexist in some photographic facilities where an automatic film processoris used under conditions where film processing operations are notcarried out continuously, e.g., as a result of variations in work loadand scheduling, resulting in periods of inactivity of the deviceshown-in FIGS. 1 and 2; and this can cause instability in the strengthof the developing liquid in tank A.

To illustrate this problem, which characterizes the prior art, FIG. 3depicts a situation where two processed film sheets (FIG. 3A) pass thephotoelectric sensor in succession with an intervening time interval tand two time-spaced sensing signals Ei, depicted respectively by curve10 and curve 11, accordingly enter the integrator in sequence. Theintegration circuit output voltage E0 resulting from the first filmsheet increases in an amount depicted by curve 10 and, upon reaching thepredetermined value, results in zeroing of the integrator and actuationof timer 8 to initiate a replenishment period (FIG. 3C), as previouslyde-' scribed. If we assume, however, that the sensing signal Eiresulting from the first film sheet has not ceased at this moment intime (e.g., because the film sheet has not yet passed completely throughthe phtoelectric sensor L-PE) the integrator output voltage E0 againrises while the replenishment control signal Es is being generated. Thenew increase in integrated output voltage E0 resulting from signalcurrent represented by the remainder of curve 10 ceases when inputsignal Ei terminates, and the value of output voltage E0 shouldthereafter remain unchanged until the second film sheet (curve 11 inFIG. 3A) reaches the photoelectric sensor, whereupon output voltage E0will again increase further.

No problem will be presented if output voltage E0 is not subject tochange during the interval 1,, between passage of the two films. Inpractice, however, the value of output voltage E0 tends to decreasegradually during interval t due to unavoidable leakage of charge fromcapacitor 4, and the effect is particularly pronounced if interval t iscomparatively long, e.g., due to intermittent operation of theprocessor. Accordingly, the value of additional output voltage E0integrated as a result of the sensing signal 11 generated by the secondfilm sheet will be lower than that which would be obtained if the secondfilm sheet hadbeen transported without any intervening time interval,and the amount of replenishing liquid added will be less than thequantity actually required. Thus, in small graphic arts establishments,where films are processed relatively infrequently, the processing liquidis not necessarily replenished in the amounts actually required, and itsactivity gradually decreases, resulting in unstable processingconditions. To prevent this, manual testing and corrective controloperations may be required, despite their undesirability in an automatedsystem.

The present invention provides a novel automatic integrator circuit andreplenishment system which eliminates the aforementioned disadvantagesresulting from possible leakage of charge from the integrator capacitor.FIG. 4 is a block diagram of one embodiment of the invention, and FIG. 5is a chart showing the operating relationships between various waveformsof the apparatus of FIG. 4.

The sensing signal Ei, developed by the blacked portion of the film asit passes through the photoelectric sensor, enters input terminal 12 andis coupled to an integration circuit consisting of resistor 13, DCamplifier 14 and capacitor 15, as described in relation to the prior artdevice of FIG. 2. According to this embodiment of the present invention,however, a reference current supplied by a separate reference currentsource 25 is selectively connected, via normally-open relay contacts 26,to the summing junction formed between resistors 13 and 27 at the inputof integration amplifier 14. This reference current is of oppositepolarity to that of the sensing signal input and acts arithmetically,when applied via switch 26, to decrease the integrated value of thesensing signal current.

The sensing signal Ei is also applied to a level detector circuit 16which produces an output signal whenever Ei is present at input terminal12, and this signal is coupled through OR circuit 17 to open thenormally closed relay contacts 19 of said integrator zeroing circuit,via relay 18, thereby removing a short circuit across capacitor andenabling signal integration to commence.

The voltage output E0 of the integration circuit constitutes the signalto level detector 20, which is similar to level detector 16 mentionedpreviously, and detector 20 produces an output signal (when voltage E0exceeds a reference level) which, via relay 21, causes the reset switchcontacts 23 of timer circuit 22 to open. Timer E1; FIG. 5B is theresulting integration circuit output voltage E0; and FIG. 5C depicts thereplenishment control, signal Er. The sensing signal Ei is produced asthe blackened portions of the film pass through the photoelectricsensor, and FIG. 5A shows sensing signals resulting from the passage oftwo such films, identified by curves 29 and 30. When the sensing signalEi shown by curve 29 first enters the system via level detector 16, itopens reset switch 19 of the integration circuit after passing throughOR circuit 17 and actuating relay 18; sensing signals Ei are thenaccumulated and integrated ouput E0 commences. As ouput E0 appears, thereset switch contacts 23 of timer circuit 22 open due to actuation oflevel detector 20 and relay 21; the timer cycle commences and, after adefinite time period T, has passed, the timer 22 causes referencecurrent switch 26, and replenishment signal switch 28, to close viarelay 24. When the reference current switch 26 closes, a referencecurrent of opposite polarity to that of the sensing signal input Ei isproduced, as previously mentioned, and is differentially integrated sothat the value of output E0 gradually decreases.

Because the time required to transport the relatively short-length filmdepicted by curve 29 through the photoelectric sensor is less than thetime interval T extablished by timer 22, the sensing signal currentshown by curve 29 falls to zero before time T, has elapsed and, due tothe differential integration action, the value of voltage E0 commencesto decrease linearly throughout time-period T reaching zero when timeperiod T,, determined by the constant discharge current flowing throughresistor 27 and the magnitude of voltage E0 at the instant when switch28 was closed, elapses. During the period T throughout which theinverted-polarity reference current is applied to the integrator, switch28 remains closed, producing replenishment signal E as shown in FIG. 5C,and the processing liquid is replenished during the time period T,.

When output voltage E0 decreases to a predetermined reference level,e.g., ground potential, the timer reset switch 23 closes via leveldetector 20 and relay 21, and the timer is reset, opening switches 26and 28 via relay 24. At the same time switch 19 in the integrationcircuit closes via OR circuit 17 and relay 18, due to the absence ofoutput from level detector 20, discharging capacitor 15 to reset theintegration circuit to its initial condition. The differentialintegration results from the constant current derived from the referencesupply 25 (and the term differential integration is employed herein toreflect this concept, even though a signal current Ei may not be presentsimultaneously with the constant reference current at the integratorinput). The replenishment time T is proportional to the integrated valueof E0, and the amount of chemical replenishment is preciselyproportional to the accumulated value of sensing signal Ei, i.e., isproportional to the blackened area of the processed film.

The foregoing example discusses the circuit action when the film beingprocessed is of a relatively short length and the input period of thesensing signal Ei is of a shorter duration than the set period T oftimer 22. Let us now consider the case in which the film being processedis of a considerably greater length, i.e., the sensing signal inputshown in curve 30 extends over a longer time period than the set periodT,, of timer 22. The device of this invention is equally applicable tothe maintenance of accuracy under either circumstance.

In the latter case even if the set time T of timer 22 has elapsed andthe inverted-polarity reference current differential integration hascommenced, the sensing signals Ei will continue to enter the system and,hence, the value of output voltage E0 will become the difference betweenthe integrated value of Bi and the integrated value of theinverted-polarity reference current In other words, if there were nosensing signal Ei subsequent to elapse of time period T,,, the output Ewould decrease at a constant rate, as shown by the inclined dotted linein FIG. B, resulting in a replenishment period of duration T But, due tothe accumulation of a succession ofsensing signals Ei subsequent toelapse of time period T,,, output voltage E0 decreases as shown by thesolid line in FIG. 58, resulting in a modified and extended replenishingperiod T Moreover, when sensing signal Ei continues to be produced evenafter time period T has elapsed (as shown in FIG. 5B), the integrationof signal E i will be resumed from the moment at which the period Tterminates, and the integrator output voltage E0 will commence to riseagain during time period T at the end of which sensing signal input Eiceases. Then, when the preset time period T again elapses, a furtherreplenishment period T will result, in response to the signal acquiredduring period T As described above, and in accordance with the method ofreplenishment disclosed by this invention, the processing liquid isreplenished in precise proportion to the exposed areas of the processedfilms. Furthermore, the timer period T set by the timer circuit isselected to be so short that the natural discharge of capacitor in theintegrator circuit can be neglected,

. resulting in precise replenishment. In this way the disadvantagesassociated with conventional replenishing devices of the prior art areeliminated, thereby contributing to a marked increase in the utilizationof automatic film processors.

Many variations will be apparent to those skilled in the art, and itmust therefore be understood that the foregoing description is intendedto be illustrative only and not limitative of the present invention.Moreover, it will be appreciated that the integrator control circuitwhich characterizes the present invention can be used in the performanceof control functions other than automatic replenishment.

Having thus described my invention, I claim:

1. A control circuit for controlling chemical replenishment in anautomatic film processor, comprisinr sensor means responsive to theimage density in a sheet of film being processed for producing a sensingsignal proportional to said density, means coupling said sensing signalto the input of an integrator means, said integrator means beingoperative to integrate said signal during a predetermined time interval,a reference source having a polarity opposite that of said sensingsignal, means responsive to elapse of said predetermined time intervalfor coupling said source to the 7 input of said integrator means tocause the sensing 55' signal already integrated by said integrator meansand any further sensing signal subsequently applied to the input of saidintegrator means to be differentially integrated and the output of saidintegrator means reduced in value toward a predetermined referencelevel, means responsive to elapse of said predetermined time intervalfor initiating flow of said replenishment chemical, and means responsiveto reduction of the output of said integrator means to said referencelevel for terminating flow of said replenishment chemical.

2. The control circuitv of claim 1 includingcontrol means responsive tocoupling of said sensing signal to the input of said integrator meansfor rendering said integrator means operative.

3. The circuit of claim 2 wherein said integrator means includes anintegrating capacitor, said control means including a shorting switchconnected across said capacitor, and signal detector means responsive tothe presence of said sensing signal at the input of said integratormeans for opening said shorting switch.

4. The control circuit of claim 1 including control means jointlyresponsive to the absence of said sensing signal at the input of saidintegrator means and to the presence of said predetermined referencelevel at the output of said integrator for rendering said integratormeans inoperative.

5. The control circuit of claim 4 wherein said integrator means includesan integrating capacitor, said control means comprising a first leveldetector having its input connected to the input of said integratormeans, a second level detector having its input connected to the outputof said integrator means, an OR circuit having inputs connected to theoutputs of said first and second level detectors, and a relay connectedto the output of said OR circuit, said relay including a pairof contactsconnected across said integrating capacitor for selectively shortingsaid capacitor to render said integrator means inoperative.

6. The control circuit of claim 1 including timer meansoperative, whenactivated, to establish said predetermined time interval, meansresponsive to the presence of a signal in excess of said reference levelat the output of said integrator means for activating said timer means,and a control relay coupled to the output of said timer means operative,upon elapse of said predetermined time interval, to close a circuitconnecting said reference source to the input of said integrator means.

7. The control circuit of claim 6 wherein said control relay is furtheroperative, upon elapse of said predetermined time interval, to close afurther circuit operative to energize a solenoid valve for initiatingsaid flow of replenishment chemical.

1. A control circuit for controlling chemical replenishment in anautomatic film processor, comprising sensor means responsive to theimage density in a sheet of film being processed for producing a sensingsignal proportional to said density, means coupling said sensing signalto the input of an integrator means, said integrator means beingoperative to integrate said signal during a predetermined time interval,a reference source having a polarity opposite that of said sensingsignal, means responsive to elapse of said predetermined time intervalfor coupling said source to the input of said integrator means to causethe sensing signal already integrated by said integrator means and anyfurther sensing signal subsequently applied to the input of saidintegrator means to be differentially integrated and the output of saidintegrator means reduced in value toward a predetermined referencelevel, means responsive to elapse of said predetermined time intervalfor initiating flow of said replenishment chemical, and means responsiveto reduction of the output of said integrator means to said referencelevel for terminating flow of said replenishment chemical.
 2. Thecontrol circuit of claim 1 including control means responsive tocoupling of said sensing signal to the input of said integrator meansfor rendering said integrator means operative.
 3. The circuit of claim 2wherein said integrator means includes an integrating capacitor, saidcontrol means including a shorting switch connected across saidcapacitor, and signal detector means responsive to the presence of saidsensing signal at the input of said integrator means for opening saidshorting switch.
 4. The control circuit of claim 1 including controlmeans jointly responsive to the absence of said sensing signal at theinput of said integrator means and to the presence of said predeterminedreference level at the output of said integrator for rendering saidintegrator means inoperative.
 5. The control circuit of claim 4 whereinsaid integrator means includes an integrating capacitor, said controlmeans comprising a first level detector having its input connected tothe input of said integrator means, a second level detector having itsinput connected to the output of said integrator means, an OR circuithaving inputs connected to the outputs of said first and second leveldetectors, and a relay connected to the output of said OR circuit, saidrelay including a pair of contacts connected across said integratingcapacitor for selectively shorting said capacitor to render saidintegrator means inoperative.
 6. The control circuit of claim 1including timer means operative, when activated, to establish saidpredetermined time interval, means responsive to the presence of asignal in excess of said reference level at the output of saidintegrator means for activating said timer means, and a control relaycoupled to the output of said timer means operative, upon elapse of saidpredetermined time interval, to close a circuit connecting saidreference source to the input of said integrator means.
 7. The controlcircuit of claim 6 wherein said control relay is further operative, uponelapse of said predetermined time interval, to close a further circuitoperative to energize a solenoid valve for initiating said flow ofreplenishment chemical.